In general, seal assemblies for a rotary bearing or the like, such as is used for sealing the wheel spindle assembly of a vehicle, are used to prevent entry of foreign material into the wheel spindle bearing, such as salt, road grime and other debris, and to prevent leakage of seal lubricant. To perform these functions, seal assemblies generally include at least one annular seal member attached to a seal casing, that in turn is biased against the opposite casing to form a sealing interface around a circular line of contact. This structure allows relative rotation between the coaxial, rotating component parts, while maintaining good sealing contact in satisfaction of the stated objective. The seals of the prior art seal assemblies are primarily formed of molded elastomer material such as rubber, but can also be made of less flexible, but lower friction materials, such as polytetrafloroethelene (PTFE).
In the recent prior art, it is common to provide both an inner and an outer annular casing with a flexible seal member supported in between. The seal member is attached to one casing and flexes against the opposite casing, and through the inherent memory of the seal material is biased into sealing contact. In this manner, the edge or lip of the seal member forms a single sealing interface along a circular line of contact. The casings are ring shaped and are formed of stamped metal with sufficient rigidity to be press fitted to respective inner and outer coaxial parts of the bearing assembly. It is also common in recent seal technology to provide seal assemblies having multiple flexible lips on a single seal member. In this manner, it is possible to provide a plurality of sealing interfaces along multiple circular lines of contact.
Although the use of flexed seal members as described above has been successful, seal assemblies that utilize this approach have been proven to be subject to some disadvantages. Especially in the area of wheel spindle technology, a seal assembly can experience rapid, axial and radial vibrations between the inner and outer casings. These vibrations can cause excessive deterioration of the seals along the circular lines of contact with the opposing casing. The deterioration can be accelerated by contact with abrasive or corrosive materials such as sand, salt or other materials that are commonly encountered in everyday use of a vehicle. Not only do corrosive materials such as salt cause deterioration to the seal structure, but as a secondary effect, it causes corrosion upon the annular lands against which the seal members rest. Rough contact between a seal lip and a corroded sealing surface results in further acceleration of the rate at which a seal member deteriorates. Once deterioration progresses sufficiently to allow contaminants to enter the bearing chamber and/or leakage of lubricant, rough bearing operation along with increased noise and heat, eventually occurs.
An example of a unitized seal assembly with multiple lip sealing members that has had success in use, but is subject to the above disadvantages, includes the seal assembly shown and described in U.S. Pat. No. 4,497,495, issued Feb. 5, 1985, and owned by the assignee of the present invention. As disclosed in this patent, the single seal is attached to the inner casing and has two lips having edges that engage the inside sealing surface of the outer casing. Corrosion of the sealing surface and/or vibration of the bearing assembly, can cause accelerated wear of the sealing edges of the lips. Eventually, this leads to deleterious seal leakage.
In addition to using flexible seal lips to engage a sealing surface, it is also known to utilize an annular diaphragm having an integral seal member with an edge that is biased into sealing contact with an adjacent sealing surface. An example of this type of seal includes U.S. Pat. No. 2,572,422 issued to Agger on Oct. 23, 1951.
The '422 patent discloses the use of an internal wave type annular compression spring to provide a strong compressive biasing force for urging an integral seal member into sealing contact with an adjacent sealing surface. This single sealing interface is formed along a circular line of contact and thus this assembly is subject to the above drawbacks. Since the sealing interface contacts the other casing along only a single, circular line of contact, vibrations of the seal assembly, as well as corrosion of the sealing surface can cause accelerated wear of the sealing edge. Thus, while this type of prior art seal assembly gives adequate levels of sealing effectiveness for short periods of time in a shielded environment, it leaves much to be desired in a hostile environment, such as encountered in protecting the bearing assembly of a vehicle wheel spindle assembly.
For the foregoing reasons and others, the need is identified to provide an improved seal assembly that is characterized by a highly effective, yet durable sealing interface. Indeed, the present invention discloses such an improvement wherein an extended area sealing surface of one or more annular disks offers a viable solution to the identified problems.